Landslides induced by the Wenchuan earthquake and the subsequent strong rainfall event: A case study in the Beichuan area of China

摘要

The Wenchuan earthquake on May 12, 2008 triggered massive landslides and a subsequent, strong rainfall prompted the development of new landslides as well as the reactivation of some pre-existing landslides. The highest seismic intensity zone of the Wenchuan earthquake in Beichuan, China was selected as a case study to analyze the influence of the earthquake and the subsequent, heavy rains on landslide evolution. We selected this study area (414 km~2) since it was close to the coseismic surface rupture and because it suffered strong ground motion. Based on the interpretation of high-resolution aerial photographs and remote sensing imagery combined with field investigation, 40 pre-earthquake landslides and 2221 coseismic landslides were identified with total landslide areas of 2.68 km~2 and 30.81 km~2, respectively. There were 134 large (over 50,000 m~2), co-seismic landslides that covered a surface area of 15.54 km~2 and represented approximately 50.4% of the total area of the co-seismic landslides. The coseismic landslides were mainly located on the hanging wall of the causative fault and on the steep, valley sides of the Jian River and its tributaries. A strong rainfall event occurred four months after the Wenchuan earthquake and induced 969 new landslides (which covered a 6.90 km~2 area) and enlarged 169 existing landslides (2.48 km~2). The landslides were identified in SPOT5 images. Ultimately, we found that earthquake tremors and the subsequent rainstorm severely disturbed the surface strata, resulting in a large number of landslides.